Projectors for laser display can generally be categorized into one of three groups: graphics projectors, beam projectors, and audience scanning projectors.
Graphics projectors are those which project logos, text and other figures onto some projection surface such as a screen. To create images, these projectors employ an X-Y scanning system, usually consisting of two small mirrors mounted on galvanometer scanners. One mirror scans the beam in one linear direction (for example, horizontally) onto the second mirror, which scans the beam in the perpendicular direction (for example, vertically). The combined X-Y motion is normally used to draw outline-type vector images, using a point-by-point “connect the dots” method, according to software commands effected by a programmable controller operably connected with the laser projector. The audience views these figures on the screen in the same way that an audience would view a movie being projected onto a screen.
A beam projector produces beams of light that are projected into mid-air. The beams are viewable in mid-air by virtue of fog, dust and moisture that either exists in the air or which is created by the performer or venue. The beams are often animated to produce a dynamic effect. The beams can be moved and animated in a number of ways. For purposes of this invention, an X-Y scanning system is also used. The scanning system may be identical to that of graphics projectors (the projector is merely aimed into the air instead of at a screen), or the scanning system may scan more slowly than that of graphics projectors (since complex images may not be required). Use of an X-Y scanning system allows flexibility to create both simple placement of the beam to hit target mirrors or objects and also to allow more complex patterns such as circles and shapes to be projected.
With both graphics and beam projectors, the generated light, typically a laser beam, never comes in contact with the audience. The light merely travels from the projector to its destination surface, or along an uninterrupted path in mid air.
Audience scanning projectors typically combine features of both graphics and beam projectors. Audience scanning projectors use X-Y scanners to project geometric figures, patterns and arrays of light beams directly into a viewing audience. As with beam projectors, when the laser is projected toward an audience, its beam also illuminates any fog, dust, and moisture in the air. The beams create dancing sculptures that are very pleasing to audience members and the beam comes in direct contact with the audience. The generated effect creates the illusion of being surrounded by a tunnel of light and by other geometric shapes that are formed by the light. One viewer has compared it to being inside a fireworks display, or at the bottom of a swimming pool filled with light. A typical audience scanning projector, as known in the art, is shown in FIG. 4. It should be noted that while audience scanning projectors are common in many foreign countries, safety considerations and legal liability have made it difficult in the U.S. to gain approval from regulatory agencies and from customers for scanning an audience.
In the case of each of the three projector types described above, the X-Y signals and beam power level signals are generated by a programmable controller which generally comprises a personal computer having suitable interface hardware, and running software for generating the images, patterns and shapes. The hardware generally includes an interface circuit board that connects to the computer. This interface circuit board includes digital-to-analog converters and voltage amplifiers, so that signals can be produced which correspond to X-Y beam positions, and to beam power levels. The X-Y beam positions and beam power levels produced by the interface hardware are sometimes referred to as “command signals,” since these signals represent the software's intention for the projector to follow. The software program generates the X-Y beam positions and beam power level “command signals” and periodically transfers these as digital data to the digital-to-analog converters in the interface circuit board. Those skilled in the art will know that any suitable interface hardware and software may be used to control any of the three projector types mentioned above. However, in the present invention preferred hardware and software systems include the QuadMod™ series of hardware boards and Lasershow Designer™ series of laser software, both from Pangolin Laser Systems, Orlando, Fla.
When projecting a laser beam toward a viewer, eye safety is a major concern. If an intense laser beam were to stop scanning and stopped directly on the pupil of a viewer's eye, retinal damage can occur if the beam has sufficiently high power and a sufficiently long dwell time. Likewise, even if the beam is not stopped but is scanned across the pupil of an eye, it can still cause retinal damage if the beam power is high enough, or if the beam is scanning slowly enough.
In audience scanning projectors in the current state of the art, the X and Y beam position signals generated by the X-Y scanners are mathematically differentiated to produce an output equivalent to X and Y beam velocity. The X and Y beam velocities are added together to produce the total beam velocity. This total beam velocity is monitored and compared to some pre-set minimum allowable velocity to make sure that the beam velocity is sufficiently high. If the beam were to stop scanning, producing zero velocity, or if the velocity were to otherwise drop below some preset threshold, this would be considered a “scanning failure.” Under a scanning failure condition, the beam may be completely turned off by the light beam modulator or by a shutter. This type of system is called a “scan-fail monitor”. Note that a scan-fail monitor is most often implemented in the form of analog signal conditioning components, but may also be implemented with computer hardware and software. A typical scan-fail monitor as know in the art is shown in FIG. 5.
While scan-fail monitors provide some level of protection for the audience, there are a number of problems that still remain. First, a scan-fail monitor does not provide automatic power level control in different regions of the scan field. For example, scan-fail monitors are not capable of allowing a higher power level over the audience's heads or below their eyes. Second, scan-fail monitors can be easily “fooled” into believing that there is a safe condition when there is not, because they only monitor the rate of change of position and do not track the actual position of the beam. For example, if the beam alternates between two fixed locations, thereby concentrating 50% of the beam power in each position, the scan-fail monitor may allow this condition since the beam is technically scanning. However, in many instances, a 50% concentration of beam power could be hazardous. Therefore, improvements are still required over the use of a scan-fail monitor alone.
The actual process of evaluating the show material being projected into an audience is an extremely time consuming task which is prone to error. The current state of the art requires a beam power meter capable of measuring irradiance (beam power per unit area), a fast silicon photodiode, an oscilloscope, a scientific calculator, and sufficient skill to use these instruments. The beam power meter must be used to measure the “static beam irradiance at the closest point of audience access”. The fast silicon photodiode and oscilloscope are used together to measure the pulse characteristics of the scanning light beam. Finally, the scientific calculator is used to perform calculations using the irradiance and pulse characteristics to evaluate whether the effect is safe or not.
While performing an evaluation of the show, each effect must be evaluated for three separate criteria, often termed maximum permissible exposure (MPE) levels, as described in well established safety standards including the IEC 60825-1 and the ANSI Z136.1. The three criteria are the single pulse MPE, multiple pulse MPE, and average power MPE. The scanning effect must not exceed any of these three MPE levels in order to be considered safe.
The terms “single pulse” and “multiple pulse” refer to a phenomenon that the human eye perceives due to the scanning action. When a laser beam scans across the pupil of the viewer's eye, it is the to deliver a pulse of laser light to the viewer's eye. This is because as the beam scans past the viewer's eye, it will only enter the eye for a brief time, depending on the beam diameter and the scan rate. This perceived pulse of light created by the scanned beam is similar to a pulse that is created by a beam which is not scanning, but is turned on for only a brief instant. The amount of time that the beam is on within the viewer's pupil is called the pulse width. For audience scanning shows, this pulse-width is typically between about 20 to 500 microseconds.
When an audience scanning effect is being projected, such as a tunnel or sheet scan, this is done by repeatedly scanning the tunnel or sheet to make it appear solid. As the beam crosses the viewer's eye, it will generate a pulse of light entering the eye. Since the X-Y scanners will trace this effect many times to make it appear to be solid, the viewer's eye may receive multiple pulses of light if the effect and viewer are stationary. The reason why pulses and multiple pulses are important, is that safety standards prescribe a maximum amount of light, that is, a maximum permissible exposure (MPE) that the viewer can be receive for a single pulse, and for multiple pulses.
During the show evaluation process mentioned above, the show must essentially be in a “paused” state while measurements can be taken, and these measurements typically require several minutes per effect. This means that if a show has hundreds of different effects, a considerable amount of time must be spent evaluating the show material. Moreover, if an effect does exceed any of the MPE levels mentioned above, the effect must be “re-programmed” so that a safe show can be produced.
There are several pieces of software on the market to aid in the task of safety evaluation and calculation of MPE levels. While the use of software in the current state of the art can remove some of the tedium and possible human error when performing many calculations, there is currently no software that can run in real time to evaluate scanning beams on the fly, and automatically reduce power levels when needed. In addition, all software programs in the current state of the art require that the user know many projection parameters which may not be readily known or easily determined, such as scan angle, actual beam diameter at the laser projector, and actual beam divergence that exists as a function of the laser and of projection system components.
The current invention completely eliminates the need for manual and tedious evaluation of the scanned laser output. Moreover, it constantly monitors a number of scanning and power related parameters and can extinguish the beam in the event an unsafe condition is detected.